Please see this guide, which explains that the information in IMDb is not updated in real time. Depending on the data type, approved contributions may appear on IMDb within one and seven days. It also tells you how to track your contributions. This page is also useful as it lists our current data processing backlogs.

If you have submitted an incorrect credit to the wrong title page you would need to submit a correction to change the title. You can do this by using the edit page feature on your name page, select Actress Credits correct/delete, hit continue. If you are unsure of the exact title you can always find it on a separate browser page, then use the ttconst from the title page. In the case of Black Mirror, https://www.imdb.com/title/tt2085059/?ref_=fn_al_tt_1 this is tt2085059. You will need to select the correct episode from the dropdown though.